Anti-Pneumocystis carinii and antiplasmodial activities of primaquine-derived imidazolidin-4-ones

Enantioselective Interactions of Anti-Infective 8-Aminoquinoline Therapeutics with Human Monoamine Oxidases A and B

8-Aminoquinolines (8-AQs) are an important class of anti-infective therapeutics. The monoamine oxidases (MAOs) play a key role in metabolism of 8-AQs. A major role for MAO-A in metabolism of primaquine (PQ), the prototypical 8-AQ antimalarial, has been demonstrated. These investigations were further extended to characterize the enantioselective interactions of PQ and NPC1161 (8-[(4-amino-1-methylbutyl) amino]-5-[3, 4-dichlorophenoxy]-6-methoxy-4-methylquinoline) with human MAO-A and -B. NPC1161B, the (R)-(−) enantiomer with outstanding potential for malaria radical cure, treatment of visceral leishmaniasis and pneumocystis pneumonia infections is poised for clinical development. PQ showed moderate inhibition of human MAO-A and -B. Racemic PQ and (R)-(−)-PQ both showed marginally greater (1.2- and 1.6-fold, respectively) inhibition of MAO-A as compared to MAO-B. However, (S)-(+)-PQ showed a reverse selectivity with greater inhibition of MAO-B than MAO-A. Racemic NPC1161 was a strong inhibitor of MAOs with 3.7-fold selectivity against MAO-B compared to MAO-A. The (S)-(+) enantiomer (NPC1161A) was a better inhibitor of MAO-A and -B compared to the (R)-(−) enantiomer (NPC1161B), with more than 10-fold selectivity for inhibition of MAO-B over MAO-A. The enantioselective interaction of NPC1161 and strong binding of NPC1161A with MAO-B was further confirmed by enzyme-inhibitor binding and computational docking analyses. Differential interactions of PQ and NPC1161 enantiomers with human MAOs may contribute to the enantioselective pharmacodynamics and toxicity of anti-infective 8-AQs therapeutics.

Synthesis, Biological Activity and In Silico Pharmacokinetic Prediction of a New 2-Thioxo-Imidazoldidin-4-One of Primaquine

The discovery of novel antiparasitic drugs for neglected tropical diseases (NTDs) constitutes a global urgency and requires a range of innovative strategies to ensure a sustainable pipeline of lead compounds. Thus far, primaquine (PQ) is the only transmission-blocking antimalarial that is clinically available, displaying marked activity against gametocytes of all causative species of human malaria (Plasmodium spp.). Chagas disease, caused by Trypanosoma cruzi, is another PQ-sensitive illness besides malaria. One of the major drawbacks of PQ is its metabolism into carboxyprimaquine (CPQ), which is less active than the parent drug. In this study, we developed different synthetic pathways to confer N-protection to PQ through introduction of thioxo-imidazolidin-4-one. The introduction of this group prevents the formation of CPQ, counteracting one major drawback of the parent drug. After that, we evaluated the potential biological activity of the novel 2-thioxo-imidazolidin-4-one derivative of PQ, which showed relevant in vitro activity against Trypanosoma cruzi (IC₅₀ 1.4 μM) compared to PQ (IC₅₀ 1.7 μM) and the reference drug benznidazole (IC₅₀ 1.6 μM). Noting its acceptable pharmacokinetic profile, this PQ conjugate may be a potential scaffold for novel drug exploration against Chagas disease.

Primaquine derivatives: Modifications of the terminal amino group

Numerous modifications of the well-known antimalarial drug primaquine, both at the quinoline ring and at the primary amino group, have been reported, mostly to obtain antimalarial agents with improved bioavailability, reduced toxicity and/or prolonged activity. Modifications of the terminal amino group were made with the main idea to prevent the metabolic pathway leading to inactive and toxic carboxyprimaquine (follow-on strategy), but also to get compounds with different activity (repurposing strategy). The modifications undertaken until 2009 were included in a review published in the same year. The present review covers various classes of primaquine N-derivatives with diverse biological profiles, prepared in the last decade by our research group as well as the others. We have summarized the synthetic procedures applied for their preparation and discussed the main biological results. Several hits for the development of novel antiplasmodial, anticancer, antimycobacterial and antibiofilm agents were identified.

Chloroquine Analogues as Leads against Pneumocystis Lung Pathogens

The impact of Pneumocystis pneumonia (PcP) on morbidity and mortality remains substantial for immunocompromised individuals, including those afflicted by HIV infection, organ transplantation, cancer, autoimmune diseases, or subject to chemotherapy or corticosteroid-based therapies. Previous work from our group has shown that repurposing antimalarial compounds for PcP holds promise for treatment of this opportunistic infection. Following our previous discovery of chloroquine analogues with dual-stage antimalarial action both in vitro and in vivo, we now report the potent action of these compounds on Pneumocystis carinii in vitro Identification of chloroquine analogues as anti-PcP leads is an unprecedented finding.

Synthesis and structure-activity relationships of carbohydrazides and 1,3,4-oxadiazole derivatives bearing an imidazolidine moiety against the yellow fever and dengue vector, Aedes aegypti

BACKGROUND

1,3,4-Oxadiazole and imidazolidine rings are important heterocyclic compounds exhibiting a variety of biological activities. In this study, novel compounds with oxadiazole and imidazolidine rings were synthesized from 3-(methylsulfonyl)-2-oxoimidazolidine-1-carbonyl chloride and screened for insecticidal activities. The proposed structures of the 17 synthesized compounds were confirmed using elemental analysis, infrared (IR), proton nuclear magnetic resonance (1 H-NMR), and mass spectroscopy.

RESULTS

None of the compounds showed larvicidal activity at the tested concentrations against first-instar Aedes aegypti larvae. However, nine compounds exhibited promising adulticidal activity, with mortality rates of ≥80% at 5 µg per mosquito. Further dose-response bioassays were undertaken to determine median lethal dose (LD50 ) values. Compounds 1, 2b, 2c, 2d, 2 g, 3b, 3c, 3 g, and 3 h were effective, with typical LD50 values of about 5 - 10 µg per mosquito against female Ae. aegypti. Compounds 2c (bearing a nitro group on the aromatic ring; LD50 = 2.80 ± 0.54 µg per mosquito) and 3 h (double halogen groups at 2,4 position on the phenyl ring; LD50 = 2.80 ± 0.54 µg per mosquito) were the most promising compounds.

CONCLUSION

Preliminary mode of action studies failed to show consistent evidence of either neurotoxic or mitochondria-directed effects. Further chemical synthesis within this series may lead to the development of new effective insecticides. © 2017 Society of Chemical Industry.

NIS-Mediated intermolecular hydroamination of allenamides with imidazole heterocycles: a facile protocol for the synthesis of allylic N,N-acetals

We report a new protocol to synthesize allylic N,N-acetal derivatives through NIS-mediated hydroamination of allenamides with imidazole heterocycles.

Crystal structure of ethyl 2-(4-chlorophenyl)-3-cyclopentyl-4-oxo-1-propyl-imidazolidine-5-carboxylate

The title compound, C₂₀H₂₇ClN₂O₃, was obtained via an original synthesis method. The central heterocyclic ring adopts a shallow envelope conformation, with the N atom bearing the cyclo­pentane ring as the flap [deviation from the other atoms = 0.442 (2) Å]. The cyclo­pentane ring adopts a twisted conformation about one of the C_N—C bonds: the exocyclic C—N bond adopts an equatorial orientation. The dihedral angles between the central ring (all atoms) and the pendant five- and six-membered rings are 10.3 (2) and 87.76 (14)°, respectively. In the crystal, C—H⋯O inter­actions link the mol­ecules into [011] chains. A weak C—H⋯Cl inter­action links the chains into (100) sheets. A mechanism for the cyclization reaction is proposed.

Peptidomimetic and organometallic derivatives of primaquine active against Leishmania infantum

The current treatment of visceral leishmaniasis is made difficult by the low efficacy, elevated costs, low bioavailability, and high toxicity of many of the available drugs. Primaquine, an antimalarial 8-aminoquinoline, displays activity against Leishmania spp., and several of its derivatives have been developed as potential antileishmanial drugs. However, primaquine exhibits low oral bioavailability due to oxidative deamination of its aliphatic chain. We previously developed peptidomimetic and organometallic derivatives of primaquine, with higher resistance to proteolytic degradation and oxidative deamination, which presented significant activity against primaquine-sensitive pathogens such as Plasmodium or Pneumocystis. In light of these relevant findings, we decided to evaluate these compounds against both the promastigote and intramacrophagic amastigote forms of Leishmania infantum, the agent of Mediterranean visceral leishmaniasis. We found that several of these compounds had significant activity against L. infantum. One of the peptidomimetic (3c) and one of the organometallic (7a) derivatives of primaquine were active against the clinically relevant intramacrophagic amastigote form of the parasite, causing >96% reductions in the number of amastigotes per 100 macrophages at 60 and 40 μM, respectively, while being less cytotoxic for host cells than the reference drugs sitamaquine and miltefosine. Hence, compounds 3c and 7a represent new entries toward the development of new antileishmanial leads.

Pneumocystis carinii expresses an active Rtt109 histone acetyltransferase

Species in the genus Pneumocystis can cause severe pneumonia in immune-compromised hosts. The identification of specific targets present in Pneumocystis species, but lacking in mammalian hosts, is paramount to developing new means to treat this infection. One such potential protein is Rtt109, which is a type of histone acetyltransferase (HAT) required for DNA replication in fungi, but not found in mammals. Sequence orthologues of Rtt109 are present in other fungi, but are absent in mammals, making it a potential pan-specific target against medically relevant fungi. Accordingly, we sought to identify the presence of an Rtt109 in P. carinii. A Pneumocystis carinii (Pc) Rtt109 165-bp partial sequence was initially identified from the incomplete P. carinii genome database. Subsequently, a full-length, 1,128-bp cDNA with homology to Saccharomyces cerevisiae Rtt109 (39% Basic Local Alignment Search Tool (BLASTP)) was cloned and characterized. Sequence analysis of PcRtt109 indicated that the P. carinii molecule contains the putative catalytic aspartate present in yeast. We further demonstrated that the PcRtt109 expressed in rtt109Δ S. cerevisiae cells restored H3-K56 acetylation and the sensitivity toward DNA-damaging agents of rtt109Δ mutant cells. Purified PcRtt109 had the ability to acetylate lysine-56 of histone H3, similar to the ability of Schizosaccharomyces pombe Rtt109 protein. The site-directed mutagenesis of PcRtt109 D84A, a potential regulatory site in the Rtt109 HAT family, abolished H3 acetylation, whereas a DD218/219AA mutation that compromised the activity of ScRtt109 had little effect, demonstrating similarities and differences in Pneumocystis PcRtt109 compared with yeast Saccharomyces cerevisiae Rtt109. These results indicate that P. carinii contains an Rtt109 HAT molecule, and represent the complete identification and characterization of a HAT molecule from this important opportunistic fungal pathogen.

Imidazoquines as antimalarial and antipneumocystis agents

Peptidomimetic imidazolidin-4-one derivatives of primaquine (imidazoquines) recently displayed in vitro activity against blood schizonts of a chloroquine-resistant strain of Plasmodium falciparum. Preliminary studies with a subset of such imidazoquines showed them to both block transmission of P. berghei malaria from mouse to mosquito and be highly stable toward hydrolysis at physiological conditions. This prompted us to have deeper insight into the activity of imidazoquines against both Plasmodia and Pneumocystis carinii, on which primaquine is also active. Full assessment of the in vivo transmission-blocking activity of imidazoquines, in vitro tissue-schizontocidal activity on P. berghei-infected hepatocytes, and in vitro anti-P. carinii activity is now reported. All compounds were active in these biological assays, with generally lower activity than the parent drug. However, imidazoquines' stability against both oxidative deamination and proteolytic degradation suggest that they will probably have higher oral bioavailability and lower hematotoxicity than primaquine, which might translate into higher therapeutic indexes.

Electrospray ionization mass spectrometry as a valuable tool in the characterization of novel primaquine peptidomimetic derivatives

Novel primaquine-derived antimalarials have been extensively characterized by electrospray ionization-ion trap mass spectrometry (ESI-MS). Experiments by in-source collision-induced dissociation (CID) in the nozzle- skimmer region (NSR) or by tandem-MS are shown to be most valuable tools for the physicochemical characterization of these 8-aminoquinolinic drugs that also bear the biologically relevant imidazolidin-4-one scaffold. It was possible to find parallelism between compound stability in the NSR and its reactivity towards hydrolysis at physiological pH and T. Moreover, tandem-MS fragmentation patterns were characteristic for each family, providing a means for structural distinction of isomers and allowing to find interesting correlations between the relative abundance of particular fragments and relevant structure-activity determinants, such as Charton steric parameter, v. In conclusion, this work provides solid grounds to establish ESI-MS as a key tool for the physicochemical characterization of biopharmaceuticals bearing the 8-aminoquinoline and/or the imidazolidin-4-one moieties.

Electrospray ionization-ion trap mass spectrometry study of PQAAPro and PQProAA mimetic derivatives of the antimalarial primaquine

Electrospray ionization-ion trap mass spectrometry (ESI-MS) of imidazolidin-4-one peptidomimetic derivatives of the antimalarial drug primaquine (PQ) is reported. These compounds contain the imidazolidin-4-one moiety either at the N- or the C-terminal of a dipeptide backbone, thus respectively mimicking PQ-Amino Acid-Proline (PQAAPro) and PQProAA derivatives of PQ. Both the peptidomimetics and precursors previously developed by us are promising drug candidates, as they were found to be active against rodent Plasmodium berghei malaria and Pneumocystis carinii pneumonia. Collision-induced dissociation (CID) and tandem-mass spectra (MS) of the title compounds, and fragmentation pathways thereof, led to the following findings: (1) CID patterns present some parallelism with the reactivity towards hydrolysis previously found for the same or related compounds; (2) a positional shift of the imidazolidin-4-one ring is reflected on both degree and pathways of fragmentation, which makes tandem-MS a key tool for differentiation of imidazolidin-4-one isomers; (3) the major MS/MS fragmentation of PQProAA mimetics involves release of a neutral diketopiperazine (DKP), in parallel to the "diketopiperazine pathway" described in tandem-MS studies of oligopeptides; (4) the relative abundance of a major fragment in tandem-MS spectra is inversely correlated with the size of the N-terminal AA in PQProAA mimetics. Overall, this work embodies an original and valuable contribution towards a deeper insight into the molecular properties of novel antimalarials, which can be viewed as representative of both the 8-aminoquinoline and, especially, the imidazolidin-4-one structural classes.